Ignition coil testing

Wilson2608

Quick question, per the FSM it states resistance should not be at zero or infinite (pin 1/2) and at zero for pin 1/3 2/3.

That’s obviously quite the range there and I see most coil packs have substantially lower resistance than the the readings I’m getting. For example, on pin 1/2 I’m getting 2000ohms and on pin 1 and 3 I’m getting 184,000 OHMs of resistance. Like holy cow! I know that the FSM says that’s within spec but is that normal ?

I’ve been trying to track down a misfire on my car for months now. Replaced MAF, tested injectors ( all at 12.4-12.6ohms) replaces air filters now I’m moving on to coil packs and spark plugs.

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Jhill

Are you chasing a single cylinder or a random misfire? To be honest I don’t put much faith in ohm testing coils, I’ve had them pass ohms test and fail in real world on other makes. The best test for a coil in my opinion is to use a HEI coil test plug. They put a fairly large load on the coil and give a nice visual and audible indication that you either are or are not getting spark, if it can fire the HEI test plug it will fire in cylinder.

SouthArk370Z

A visual inspection of the spark plugs should tell you if any of the coil packs aren't firing properly. If it's a random misfire, it's probably not a coil/plug problem.

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Wilson2608

Chasing a random misfire. I’m starting to think it has something to do with my PCV system(oil residue and dirt/grime all over valve cover) . Car has 120k miles on it and I’ve had this misfiring issue for 6-7 months if not more now. The misfire is noticeable at WOT and idle. Under light loads the car drives perfectly fine .

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Wilson2608

Thanks for the reply, I agree the coil packs are probably not the issue now that I’ve inspected them as well. Not bubbling or burnt wiring smell and they all appear to be within specs.

It is a random misfire that I’ve had for a long time now. At idle and WOT the misfire is horrific. At WOT it’s missing so bad that the car jerks constantly. At partial throttle you would never know anything is wrong. Any suggestions on where to go from here ? I’m going to replace the PCV valves as the car has 120k miles on it and i do see some oil residue near one valve. Injectors and fuel pressure is good, coil and spark appear to be good, i do have some old *** air filters that I’m going to clean and see if that helps. No codes beside p0300

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Stillen G3, z1 Intake Manifold, Stillen Headers, Z1 HFC's, Stillen Catback. 330whp 267 ft- lbs tuned at Z1 motorsports.

SouthArk370Z

When was the last time you cleaned your MAFs? May not be your problem but it's a very easy job and probably needs to be done anyway - screwdriver, MAF spray, and about 5 minutes per side. At least one DIY thread on this site.

Edit: If your air filter is more than 2-3 years old, go ahead and replace it.

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Wilson2608

Went ahead and ordered new filters and will clean the MAFs just in case. I hopefully think I figured out the issue. Inspecting spark plugs showed fresh oil covered all over the plug threads, replacing spark tube seals and valve cover gaskets. I’m hoping the oil caused the misfire.

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JSON

Any updates? I'm having random misfire out of the blue. Changed all spark plugs and cleaned TB to no avail. Wondering if a coil pack is bad, because car is vibrating even at idle like a cylinder isn't firing. Only P0300 tho

tjlazer

I'm getting them all the time when it's cold out. Car drives fine and the code clears itself after a while of driving.

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Jhill

I’d be looking more at the fueling side of things.

Tractionless

Ignition coils that test fine static off the car can still be bad when put under load during normal operation. You may never see it test "bad" on a multimeter.

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1slow370

The fsm sucks when it comes to coils. It should just say "replace all coils with known good ones, and check to see if the light goes out. Our misfire detection sucks, and there is no way to determine if a self ignited coil has a bad winding. It can only be checked for a shorted, burned out ignitor, good luck it's probably not the coils any way see other sections"

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SonicVQ

The FSM is written for a tech to be as fast as possible and in the process, if more parts can be sold, that is good for the dealer. Years ago my friend had to replace all 6 coils on his 95 Maxima as the dealer couldn't figure out which one was bad.

As for the coil testing, there are a few tests the FSM doesn't mention...
They do require a scope (mine is a $125 Pico 2204) and you simply view the primary current and voltage waveform of the common ground for all 6 coils. Since you see all 6 coils in operation, you can see the weak one.

For the misfires, the fuel trims can help narrow it down to a specific bank, and the mode $06 misfire counters can help you narrow it down further...

Then scoping the fuel injector current (not easy to do on the VQ37) can how how well they are working and even when the fuel injector is actually opened. (google pintle bump)

The VQ37 is a fairly simple engine, and deeper troubleshooting requires special tools, or take it to a shop with the required skills and tools.

Bonus Tip
You can also use a scope to measure fuel pump RPM!
For a Nissan/Infiniti simply measure the ripple voltage frequency and multiply it by 7.5.
My pump runs at 6200 RPM at idle

1slow370

But since most nissan dealer techs can't do any of that it sucks. Replace with known good part, check for for frayed or burnt wires, move to a different subsystem if still misfiring. That's literally all it has to say under coils

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JARblue

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